1. Technical Field
The present invention relates to electron beam lithography. In particular, the present invention relates to the creation and use of modulated electromagnetic radiation, typically ultraviolet radiation modulated by a spatial light modulator, impinging on a photocathode to form multiple beams of electrons, increasing thereby the throughput of electron beam lithographic systems.
2. Description of Related Art
Electron beam (xe2x80x9ce-beamxe2x80x9d) lithography is a commercially important technique for patterning by directing a beam of electrons onto a substrate coated with a suitable resist. Development of the exposed resist followed by etching leads to the selective removal of material and creation of the desired pattern in regions exposed to electron impact (positive resists) or in regions not exposed to electron impact (negative resists). A common application of e-beam lithography is to manufacture the masks for use in photolithography, although direct e-beam exposure of an integrated circuit wafers and other targets is also performed.
Exposure of the resist is typically carried out by the direction of one or more focused beams of electrons onto the resist-coated substrate. Control of the electron optics (typically computer control) allows the process designer to direct the e-beam to the regions of the substrate requiring exposure, to compensate in beam deflection for mechanical translations of the stage containing the substrate, to scan or tile the substrate in the desired pattern, to control the dose of electrons impacting any particular pixel on the substrate (off, on or gray scales), and otherwise to direct the location and dose of e-beam impact to create the desired pattern. In addition to focused-beam lithography, projection e-beam lithography (xe2x80x9cSCALPELxe2x80x9d and the like) are also being used. (See, for example, Yamashita et. al. Jpn. J. Appl. Phys. Vol 35 (1996) pp. 6404-6414 and Sohda et. al. J. Vac. Sci. Technol. B 13(6), November/December 1995 pp. 2419-2423). To be definite in our discussion, we will describe in particularity the patterning of a substrate by e-beam lithography using a plurality of focused electron beams. However, the present invention relating to the creation of multiple beams of electrons is not inherently limited to focused-beam lithography and generalizations to other areas of technical applicability will be apparent to those having ordinary skills in the art based upon the descriptions contained herein.
One significant drawback to lithography performed by means of a focused beam of electrons is the relatively low throughput obtainable in comparison with photolithography performed by exposure through a mask. It may require several hours (perhaps as many as 30 hours) to fully expose a substrate to e-beam impact. The e-beam equipment must function properly and continuously throughout this process. Equipment failures during exposure lead to rejection of products, a reduction in average throughput and further increases in overall costs. Thus, various means have been proposed for accelerating e-beam lithography, one of which relates to the use of multiple focused beams of electrons directed in parallel onto the substrate. See, for example, Groves et. al. (U.S. Pat. No. 5,981,962); Lin et. al. (U.S. Pat. No. 5,539,568), Mueller et al.(U.S. Pat. No. 4,856,037) and references cited therein. A recent review of electron projection display technology is given by Hornbeck in TI Technical Journal, July-September 1998, pp. 7-46.
The present invention generally relates to sources and means for creating multiple beams of electrons by directing suitably modulated light onto a suitable photocathode. Other sources of multiple parallel beams of electrons are described, for example, in the work of Schneider and co-workers (J. Vac. Sci. Technol. B 14(6), NovemberDecember 1996 pp. 3782-3786 and J. Vac. Sci. Technol. B 15(6), NovemberDecember 1997 pp. 2702-2712), Baum (U.S. Pat. No. 6,005,247), MacDonald (U.S. Pat. No. 5,363,021) and Engle (U.S. Pat. No. 5,557,177) and references cited therein.
The present invention also generally relates to the use of spatially modulated patterns of light impinging on a photocathode to create multiple sources of electrons at the photocathode. The multiple e-beams thus created impinge on the acceptance cone of a suitable focusing column(s), creating thereby multiple beams of focused electrons for lithography. Techniques and equipment for modulating light include the work of Hara et. al. (U.S. Pat. Nos. 4,741,602; 4,763,996; 4,818,983), Kobayashi et. al. (U.S. Pat. Nos. 5,170,281; 5,208,696), Kato et. al. (U.S. Pat. No. 5,173,954) and Sandstrxc3x6m (PCT International Publication No. WO 99/45441) and references cited therein. Other examples of modulated and/or patterned light include the work of Sweatt (U.S. Pat. No. 5,920,380) and Culkin (U.S. Pat. No. 5,543,862) and references cited therein.
The present invention relates to the creation and use of modulated electromagnetic radiation, typically ultraviolet radiation modulated by a spatial light modulator, impinging on a photocathode to form multiple beams of electrons, increasing thereby the throughput of electron beam lithographic systems.
Electron beam exposure of a resist for patterning is typically carried out by the direction of one or more focused beams of electrons onto the resist-coated substrate. Control of the electron optics (typically computer control) allows the process designer to direct the e-beam to the regions of the substrate requiring exposure, to compensate in beam deflection for mechanical translations of the stage containing the substrate, to scan or tile the substrate in the desired pattern, to control the dose of electrons impacting any particular pixel on the substrate (off, on or gray scales), and otherwise to direct the location and dose of e-beam impact to create the desired pattern. A drawback to lithography performed by means of a focused beam of electrons is the relatively low throughput obtainable in comparison with photolithography performed by exposure through a mask. Thus, various means have been proposed for accelerating e-beam lithography, one of which relates to the use of multiple focused beams of electrons directed in parallel onto the substrate.
The present invention generally relates to sources and means for creating multiple beams of electrons by directing suitably modulated light onto a suitable photocathode. The present invention also generally relates to the use of spatially modulated patterns of light impinging on a photocathode to create multiple sources of electrons at the photocathode. The multiple e-beams thus created impinge on the acceptance cone of a suitable focusing column(s), creating thereby multiple beams of focused electrons for lithography. The present invention provides a source of multiple beams of electrons having a desired spatial pattern, as typically used for multiple beam lithography. A source of radiation, typically ultraviolet radiation, is directed onto a modulator and from the modulator onto a photocathode. The modulator, typically a spatial light modulator, imposes a spatial pattern onto the radiation. The pattern imposed onto the radiation is transmitted to the multiple beams of electrons as such beams are generated by the photocathode. An electron beam lithography system having higher throughput than conventional single beam systems is one result. Methods of creating multiple electron beams and methods of patterning targets with such multiple beams of electrons are also described. A micromirror array is a preferred modulator. Mercury arc lamp directing ultraviolet radiation by means of the modulator onto a cesium telluride photocathode is a preferred combination of radiation source and photocathode.